since vs thereof

since

adv
  • From a specified time in the past. 

prep
  • At certain points during that period of time. 

  • Continuously during that period of time. 

conj
  • Because. 

  • From the time that. 

thereof

adv
  • From that circumstance or origin; therefrom, thence. 

  • Of this, that, or it. 

How often have the words since and thereof occurred in a corpus of books? (source: Google Ngram Viewer )